Raised pavement marker

The orange markers separate opposing traffic lanes.

A raised pavement marker, also known as a Botts' dot, delineator, or simply a reflector, is a safety device used in road construction in the United States and Australia as well as other countries.

Most regions of the United States use plastic devices with two angled edges facing the drivers with a corner reflector strip. They are placed in a small indentation in the pavement in areas where snow plowing is frequent. The devices can be seen from a great range and come in three colors, as follows:

• White markers — for lane markings and the shoulder. These sometimes have a red strip on the opposite side to notify drivers of their incorrect direction of travel.
• Yellow markers — found on the left signifying the traffic direction change, or a median. They are also sometimes used on the shoulder.
• Blue markers — Usually used to mark the location of fire hydrants.

Colors can also be combined, with a different color facing each direction:

• White and red — white for marking lane divisions in one direction, and red to indicate 'do not enter' in the other direction
• White and black — white for marking lane restrictions (such as an HOV diamond) in one direction on a roadway that has 'reversible' traffic flow, and black in the other direction when the markings don't apply

The current trend for lane markings is to intersperse retroreflective paint lines with reflectors as seen on the majority of American highways.

The design now used widely throughout the United States was invented by engineer Sidney A. Heenan in the course of his employment with the Stimsonite Corporation in Niles, Illinois. Heenan filed an application for a patent on October 23, 1964. Patent No. 3,332,327 was subsequently granted on July 25, 1967.

Stimsonite went on to become the leading manufacturer of raised pavement markers in the United States and was acquired in the mid-1990s by Avery Dennison Corporation. Today, Avery continues to sell the devices created by Heenan under their Sun Country brand of raised pavement markers.

Botts' dots

Botts dots on Interstate 280 (California), near the Sand Hill Road exit

This picture illustrates how Botts dots can be used to replace the double yellow paint stripes in the median.

File:Squarebottsdot.jpg

Square Botts dot

File:Roundbottsdot.jpg

Round Botts dot

In the U.S. state of California, similar objects called Botts' dots are used to mark lanes on state highways and many arterial roads. They are named after Dr. Elbert Dysart Botts, a California Department of Transportation (Caltrans) engineer credited with overseeing the research that led to the development of the markers and the epoxy used to attach them to the road.

They come in two varieties: rounded white markers used for lane dividers; and square, colored, reflective markers used for other situations. Of the square markers, white markers are used (between clusters of the round markers) to indicate lane lines (often with red "wrong way" reflectors on the back side), yellow markers to separate traffic directions, and blue to locate fire hydrants. The round markers are made out of clay, plastic, or polyester, while the square markers are made out of plastic.

Over the years, Caltrans has wavered back and forth between using asphalt and concrete for new freeways. The current trend is to use concrete, but since white Botts dots are hard to see on white concrete through sun glare, Caltrans has often been forced by public demand to paint lane stripes on freeways that run east-west (and thus face the sunrise or sunset).

Also, Botts' dots are rarely used on freeways in regions where it snows because snow plows scrape them off. On such freeways in California, Caltrans solved this problem by using lane stripes in place of the round markers, and by carving little "dips" in between the stripes for the square markers so that the snow plows go straight over them. The small dips also provide an even larger "bump" than Botts' dots alone. Many other states use the same method.

As seen in the photograph to the right, some wealthy American cities are able to replace lane stripes with Botts' dots altogether, so that paint is used only for turn arrows and crosswalks at intersections.

History

According to journalist Mark Stein, Caltrans records indicate that its personnel may have been speculating about the concept of raised pavement markers as early as 1936. However, the department did not commence research in earnest until 1953, when the postwar economic boom resulted in an alarming increase in the number of cars and car accidents in California^[1]. Painted lines tended to become invisible during rain, and the task of applying paint exposed Caltrans workers to dangerous traffic situations.

Botts was born in Missouri in 1893 and was an assistant chemistry professor at San Jose State College when he was recruited to Caltrans^[2]. He is credited with leading the division of the Caltrans research laboratory (Translab) that conducted the initial research into identifying the best shapes and materials for raised pavement markers^[3]. Much of the necessary field research was conducted by his team on a new freeway in West Sacramento in the spring of 1955^[4]. Although the initial goal was to improve lane visibility, it was at this point that the tactile feedback provided by the dots was discovered^[5].

The initial dots were made out of glass^[6] and were attached by nails or tacks to the road, as suggested by Botts^[7]. The nails were soon abandoned; his team discovered that when the dots eventually popped out under stress, the nails would puncture tires. Contrary to a common myth^[8], the published record does not make clear whether Botts invented the famous epoxy that solved the problem^[9]; some sources indicate that one of his proteges was responsible for the epoxy^[10].

Botts never lived to see the success of his research. He died in April of 1962 and his work on the dots was filed away; it was not even mentioned in his obituary in Translab's internal newsletter^[11]. Two years later, his research was rediscovered when his division (now under the direction of Herbert Rooney) decided to conduct further research into raised pavement markers. At this time, Translab developed the modern pattern of interspersing plastic square reflectors between groups of four round polyester or epoxy dots. This pattern was first tested along Interstate 80 near Vacaville in 1965. To minimize the risk that dots would become coated with rubber scraped off tires, Translab switched to clay round markers in 1966^[12].

In September of 1966, the state Legislature mandated that Botts dots were to be used for lane markings for all state highways except in areas where it snowed in the winter^[13].

Today, there are more than 25 million Botts dots in use in California^[14].

References

^ Cave, Kathryn. "State lab in fast lane of high-tech road gadgets." The Orange County Register, 21 October 1991, sec. A, p. 1.

^ Haldane, David. "Dots' Demise Denied." Los Angeles Times, 7 March 1997, sec. B, p. 1.

^ Martin, Hugo. "Behind the Wheel: The Botts Dot's Future May Hit a Bump in the Road." Los Angeles Times, 23 October 2001, sec. B, p. 2.

^ Richards, Gary. "It May Be End Of Road For Noisy Botts Dots." Contra Costa Times, 18 January 1997, sec. A, p. 3.

^ Rubenstein, Steve. "Caltrans Plots To Erase Lots Of Botts Dots." San Francisco Chronicle, 18 January 1997, sec. A, p. 13.

^ Stein, Mark A. "On the Button: The Quest to Perfect Botts' Dots Continues." Los Angeles Times, 11 August 1991, sec. A, p. 3.

See also

• Cat's eye (road) - a similar device invented in the United Kingdom and patented in the United States in 1939 [15]

External links

• Caltrans Botts' Dots fact sheet
• Avery Dennison Reflective Products Division - the leading manufacturer of raised pavement markers